A multichannel spectrometer is a device comprising a scintillation crystal, a multiplier phototube, an electronics amplifier and a multichannel analyzer, for detecting various kinds of radiation rays and performing nuclide identification. The basic principle of the multichannel spectrometer lies in that: the scintillation crystal absorbs (or partially absorbs) the radiation rays, emits light and focuses the light into the multiplier phototube which performs a photo-electric conversion of the light, and linearly multiplies the converted electric signal into an electric pulse; the electronics amplifier shapes and amplifies the electric pulse, and transfers the processed electric pulse to the multichannel analyzer which analyzes the electric pulse and converts it into a digital signal. The above process is a process of linear amplification and conversion, thus, the multichannel analyzer can be used to detect a spectrum of incident radiation rays and perform nuclide identification.
Among the scintillation crystals, the NaI scintillation crystal is still the most broadly used scintillation crystal due to its high light yield, high detection efficiency and good energy resolution. Therefore, a NaI multichannel spectrometer comprising a NaI scintillation crystal is an important tool for monitoring radioactive substance, and identifying and analyzing nuclide.
However, in a NaI multichannel spectrometer, luminous efficiency and light transmission efficiency of the NaI scintillation crystal, performance of the multiplier phototube, gain of the amplifier, stability of the high voltage, etc., are greatly affected by changes in the environmental temperature and humidity. Therefore, the shape and peak position of a radiation ray spectrum measured by the NaI multichannel spectrometer will be shifted and distorted under the influence of these environmental factors. Thus, it is generally required to recalibrate the spectrometer using a standard radioactive source.
In the prior art, recalibration is performed generally by using a method of internal calibration with a radioactive source, such as doping a small amount of radioactive nuclide in the crystal; or using light emitted by an LED to simulate the radiation rays processed in the spectrometer. In addition, there are some other existing technologies which use a characteristic peak in a natural background spectrum to perform artificial recalibration. However, all of these technologies for recalibration have a shortcoming of being unable to perform real-time monitoring of peak shift, and since the recalibration usually involves using of standard radioactive sources, it further has a problem that it requires the strict management of these standard radioactive sources.